Typically, a powered-up computer consumes a great deal of energy to drive its video display and other electronic components such as hard disk drives. Unfortunately, due to the way many computers are used, a significant part of the power they consume is wasted. For example, many computer users leave their machines powered-up twenty-four hours a day to avoid the delay required to boot up the computer from a "cold-start" (when the computer is powered-on from a fully-off state). Also, even during work hours, a computer may idle for hours at a time.
This waste is expensive and it also exacts a toll on the battery life of increasingly-popular laptop computers. Consequently, there is a demand for computer systems that meet the strict power consumption guidelines established by recently adopted industry standards, such as the Energy Star program. Among the wide range of possibilities for reducing computer power consumption there are two principal approaches. First, computers could be built from components based on new, energy efficient technologies; for example, low voltage microprocessors and flat panel LCDs. The chief disadvantage with this approach is expense. Second, in computer systems using mainstream technology, the power used could be dramatically reduced through smarter management of the power system. The following discussion will focus on the second approach.
A typical prior art approach to smarter management of the power used by a computer provides for digital control of the power system. This allows the central processing unit (CPU) to automatically place an idling, fully powered-up computer in a low power standby state, or a user to do the same via remote power control switches. This feature is called "soft off." The prior art also provides a "soft on" feature, which allows the user to restore full operational power from the standby state by activating one of the aforementioned remote power control switches.
Allowing the user to remotely trigger a soft on event (e.g., from a keyboard) requires the power system to supply housekeeping power to at least the remote soft on/off switch(es) and the CPU while the computer is in the standby state. To enable the power system to efficiently supply the housekeeping power in the standby state and the full power required when the computer is in the operational state, the prior art has adopted a two converter arrangement. During normal operation, the main power converter supplies the full power needs of the computer. When the computer system is placed in the standby state, the main converter is switched off and an auxiliary converter switched on to supply a small amount of housekeeping power for the CPU and any other components required for the soft on function. This solution reduces energy consumption, but adds complexity and cost to the power system due to the presence of the two power converters.
A simpler and less expensive solution would ideally utilize a single, always-on power converter to provide both operational and housekeeping power. In such a system, the prior art soft off and soft on features would be provided by respectively switching off and on the power converter's outputs to all but those components nonessential to housekeeping functions. However, using a single converter in this fashion creates a power supply problem not present in energy efficient, two converter power systems.
In a typical AC powered computer system, a mechanical power control switch energizes the inputs of an on-board AC to DC power converter, resulting in the converter's DC output rising gradually from off to fully-on. This gradual cold start turn-on, which is optimal for electronic computer components, is also present in energy efficient two converter systems following a soft on event due to the main converter's being switched on to restore full operational power.
However, in a one converter system where the single converter is always left on, merely switching the always-on converter's outputs results in a rising edge to the DC power signal that approximates a step function. Supplying such a stepped power signal to the large integrated circuits (ICs) that comprise a computer system could result in IC latchup problems.
For the foregoing reasons, there is a need for an efficient, digitally controlled power system having one always-on converter that supplies the computer's electronic components with a DC output signal whose rising edge following a soft on event resembles the gradual rising edge of the DC power signal of the converter following a cold start.